Field of the Invention
The present invention relates to an image reconstructing apparatus, an image constructing method, and a non-transitory computer-readable storage medium and, more particularly, to a technique of outputting the image quality of an image obtained by iterative reconstruction.
Description of the Related Art
An imaging apparatus acquires a plurality of images from different angles, and creates a reconstructed image from these images using a technique called an image reconstructing method. As image reconstructing methods, methods called a filtered back projection method and iterative reconstruction have been described in the Handbook of Medical Imaging, Medical Imaging Technology, in 2012.
Among others, the iterative reconstruction is an image reconstructing method of performing calculation by repeating forward projection for calculating a projected image from a reconstructed image obtained by back projection (to be described later) and back projection for calculating a reconstructed image from the projected image. This reconstructing method calculates a coefficient by comparing the projected image obtained from the reconstructed image with an image acquired by an imaging apparatus, and performs back projection using the coefficient. Therefore, the image quality of a reconstructed image changes every time calculation is repeated. In this reconstructing method, it is expected to obtain the effect of obtaining a less noisy image while maintaining the sharpness. However, if repetitive calculation is excessively performed, an attempt to reproduce noise in a acquired image is made, thereby unwantedly increasing noise.
Japanese Patent Laid-Open No. 2006-25868 describes a method in which when performing reconstruction by iterative reconstruction, a region of interest is set on a reconstructed image as an intermediate result, and it is determined based on the standard deviation of the region whether to further perform calculation.
There are various applications and purposes of reconstructed images, which require different image qualities. It is, therefore, necessary to construct a system that can satisfy the requirements.